220 
Bugs, Cicadas, Aphids, and Scale-insects 
present), which, when the insect is at rest, are laid back along the abdomen 
unfolded, and parallel or slightly overlapping at the tips. Only about forty 
species are yet known in this country, but as practically only one entomol¬ 
ogist has attempted to make a systematic study of the group and his speci¬ 
mens were mostly collected in a single locality (Amherst, Massachusetts), 
it is certain that many species are yet to be found and named. This 
entomologist, Hinds, has published in a recent paper (Contrib. to a Mon¬ 
ograph of the Thysanoptera of N. A., Proc. U. S. Nat. Mus., vol. xxvi, 
1902) practically all that is known of our American species, and I have 
largely drawn on his paper for the present short account. 
Although the thrips used to be classified as a family of the order Hemip- 
tera, they are now, and rightly, assigned to an order of their own, called 
Thysanoptera (fringe-wings). This separation is due to the peculiar charac¬ 
ters of their mouth-parts and of the feet, and 
to the interesting character of their develop¬ 
ment, which is apparently of a sort of tran¬ 
sitional condition between incomplete and 
complete metamorphosis. The food of the 
thrips is either the sap of living plants or 
moist, decaying vegetable matter, especially 
wood and fungi. The mouth-structure in ac¬ 
cordance with this food habit is of a sucking 
type, with mandibles and maxillae modified to 
be needle-like to pierce the plant epidermis. 
But the mouth-parts are curiously asym¬ 
metrical, the right mandible being wholly 
wanting and the upper lip being more ex¬ 
panded on one side than the other (Fig. 308). 
The peculiarity in the life-history consists in 
a quiescent, non-food-taking stage like the 
pupal stage in insects of complete metamor- 
n TT , , phosis, but before reaching this stage weil- 
parts, much enlarged, of developed external wing-pads have appeared, 
thrips. ant., antenna; lb., j ust as happens in the case of immature 
labrum; md., mandible; mx., . - . , , , 1 
maxilla; mx.p., maxillary pal- insects of incomplete metamorphosis. Finally, 
pus; li.p., labial palpus; m.s., the peculiar character of the feet is due to the 
much^enlarged.) ^ Presence of a small protrusile or expansile 
membranous sac or bladder at the tip of the 
tarsus, instead of claws or fixed pads, which seems to play a not well 
understood function in the holding on by the insect to the leaf or 
flower parts which it may have occasion to visit. The bladder seems 
ms. 
